Do you have gas or diesel air heaters for 24v or 48v systems or only 12v?
Velit gas or diesel air heaters run on 12V but you can get stepdown converters for use with 24v or 48v systems.
Never hook Velit air heaters directly up to 24V or 48V power. Typically this would just blow the fuse but can also cause further electrical damage to wiring or ECU components.
The follow is just suggested guidance and you should consult and electrical engineer to ensure the setup is right for your specific application.
If your rig is built on a 24v or 48v system - You'll need to step that power down to 12V for the air heater power source. You will want to ensure the converter can deliver at least 20amps of 12v power, ideally 30A to ensure proper power with conversion. This is because glow plug heating can sometimes call for over 15amps of power. You'll also need to consider any other 12v accessories and their draw if you are powering more than just the air heater with the converter.
24v to 12v 30amp converter: https://a.co/d/0cZx9Us7
48V to 12V 30amp converter: https://a.co/d/00VoXQ7i
We recommend using a multi-meter to confirm output voltage before connecting air heater wiring harness.